1. Technical Field
The present invention relates to a photoconductor preventing background fouling well, and to an image forming method and an image forming apparatus using the photoconductor.
2. Description of the Related Art
Typically, image forming apparatuses such as printers, copiers and facsimiles using electrophotographic methods form images with a series of processes, i.e., charging, irradiating, developing, transferring and cleaning.
Means of performing such image formation include at least a charger, an image irradiator, an image developer (particularly a reverse image developer), a transferer, a cleaner and a photoconductor.
Such image forming apparatuses produce deteriorated images having grayish background when continuously used for long periods. When such images having background fouling are produced, the photoconductor is replaced with a new one.
Recently, print cost reduction and improvement of environmental performance have been demanded, and therefore photoconductors are required to have higher durability.
Constitutions or materials included in an intermediate layer between an electroconductive substrate and a photosensitive layer are changed, or an anodized film is formed on the surface of the electroconductive substrate as above to prevent holes from injecting into the photosensitive layer or a charge generation layer from the electroconductive substrate in reverse developing, which causes black spots. For examples, the following electrophotographic photoconductors are known:
(1) an electrophotographic photoconductor including an electroconductive substrate, and at least an undercoat layer formed of a resin including a heat-treated titanium oxide and a photosensitive layer thereon;
(2) an electrophotographic photoconductor including a substrate, and an undercoat layer including titanium oxide having an average primary particle diameter not greater than 0.4 μm and a thermosetting resin in a volume content of from 0.5 to 0.6 and a photosensitive layer thereon;
(3) an electrophotographic photoconductor for reverse developing, including an electroconductive substrate formed of aluminum or an aluminum alloy, and an anodized layer having surface peak intervals Sm of from 0.3 to 250 μm, a maximum height Rt of from 0.5 to 2.5 μm and a surface glossiness not less than 60 gloss, and a photosensitive layer thereon;
(4) an electrophotographic photoconductor including an electroconductive substrate, a photosensitive layer and an intermediate layer including a fine powder of titanium oxide on the surface of which zirconium oxide is present therebetween; and
(5) an electrophotographic photoconductor including an electroconductive substrate, a photosensitive layer and an undercoat layer formed of a resin in which anatase-rutile mixed crystal titanium dioxide therebetween.
In order to improve background fouling, it is effective to form an intermediate layer on an electroconductive substrate of the photoconductor and a photosensitive layer thereon, which is a typical art. Various arts such as material constitutions and surface profiles of a photoconductor including an electroconductive substrate, and an undercoat layer and an intermediate layer overlying the substrate are disclosed to improve background fouling.
As a disclosure on the material constitutions, a photoconductor including an undercoat layer and an intermediate layer including a specific metal oxide such as titanium oxide is known.
Japanese Patent No. JP-4570155-B2 (Japanese published unexamined application NO. JP-2007-470467-A) discloses an electrophotographic photoconductor including an electroconductive substrate, and an undercoat layer, an intermediate layer and a photosensitive layer overlying the substrate this order. The undercoat layer two metal oxides having average particle diameters different from each other and a thermosetting resin, and the intermediate layer includes an organic metallic compound as a main component. This maintains good environmental stability and production of high-quality for long periods, and further prevents leak due to pin holes keeps good electrical properties even when used in a contact charger, and can be downsized.
Japanese Patent No. JP-3999074-B2 (Japanese published unexamined application NO. JP-2003-162080-A) discloses an electrophotographic photoconductor including an intermediate layer. The intermediate layer is formed by a coating liquid including an organic solvent, and a binder resin and titanium oxide dispersed therein. The titanium oxide has a specified average particle diameter to prepare a coating liquid having good coatability without defective coating and good stability. The resultant photoconductor produces high-quality images without defective images.
Japanese Patent No. JP-3878445-B2 (Japanese published unexamined application NO. JP-2003-98705-A) discloses an electrophotographic photoconductor including an electroconductive substrate, and an intermediate layer and a photosensitive layer thereon. The intermediate layer includes two titanium oxides and a binder resin, and a ratio of an average particle diameter of each of the two titanium oxides is specified for the electrophotographic photoconductor to produce high-quality images without defective images and have good durability.
Japanese published unexamined application NO. JP-2003-270808-A discloses a method of preparing an undercoat layer coating liquid for electrophotographic photoconductor, in which a particulate metal oxide and a binder resin are dispersed. From the beginning of dispersion process, a mixed solvent of a circular ketone solvent and a side-chain ketone solvent such as methyl ethyl ketone and cyclohexanone to dissolve a resin is added, and a metal oxide such as a titanium oxide or a surface-treated titanium oxide is wet pulverized. The undercoat layer coating liquid having good dispersibility, temporal stability, and coatability on an electroconductive substrate to form a uniform undercoat layer.
Japanese published unexamined application NO. JP-2004-037482-A discloses a method of producing an electrophotographic photoconductor including a substrate, and an undercoat layer and a photosensitive layer thereon. An undercoat layer coating liquid (a dispersion solvent is, e.g., methyl ethyl ketone and cyclohexanone) used for forming the undercoat layer by spray coating includes a metal oxide such as a titanium oxide or a surface-treated titanium oxide. The metal oxide has a specific sedimentation speed for preventing a spray nozzle, a filter and pipings from being clogged to improve productivity, and preventing coating defects such as uneven coating.
Meanwhile, modifying the surface profile is known as a method of improving background fouling.
Japanese published unexamined application NO. JP-2006-053577-A discloses a method of sampling a cross-sectional curve of an interface of a photosensitive layer at a substrate side in a horizontal direction and subjecting data of the height of the cross-sectional curve to a discrete Fourier conversion. Plural peaks in a specific area prove the photoconductor does not produce stripe-shaped images or light and shade stripe-shaped images, and an image forming apparatus using the photoconductor is capable of producing high-quality images.
Japanese published unexamined application NO. JP-2011-002480-A discloses a method of measuring a concave and convex shape of the surface of an electrophotographic photoconductor with a surface roughness/profile measurer to obtain a one-dimensional data array, subjecting the one-dimensional data array to a wavelet conversion and multi-resolution analysis to separate into six frequency components from high frequency to low frequency. Further, arithmetic mean roughness of total 12 frequency components including other six frequency components obtained by a specific method have specific relationships each other to improve acceptability of the electrophotographic photoconductor to a lubricant, prolong lives of the electrophotographic photoconductor and an image forming apparatus using the photoconductor, and reduce print cost.
Japanese published unexamined application NO. JP-2012-063720-A discloses a method of measuring a concave and convex shape of the surface of an electrophotographic photoconductor with a surface roughness/profile measurer to obtain a one-dimensional data array, subjecting the one-dimensional data array to a wavelet conversion and multi-resolution analysis to separate into six frequency components from high frequency to low frequency. Further, arithmetic mean roughness of total 12 frequency components including other six frequency components obtained by a specific method have specific relationships each other to provide just a required quantity of a lubricant to electrophotographic photoconductor when necessary, highly stabilize cleanability thereof, and high-quality images are produced thereby.
Japanese published unexamined application NO. JP-2005-031433-A discloses an electrophotographic photoconductor including an electroconductive substrate, and an undercoat layer and a photosensitive layer thereon, which is installed in an image forming apparatus using coherent light as an irradiating light to form an image. An arithmetic mean roughness and a maximum surface roughness of the surface of the undercoat layer, which are measured by a probe-type surface roughness meter are in specific ranges to produce uniform quality images without interference fringes and print defects such as black spots.
However, these conventional arts do not realize an intermediate layer producing higher quality images and having higher durability.